Week 07 - Computer-controlled machining


CNC milling

For this week we will use a powerful CNC router (EasyWorker - Master Pro 2513)for computer-controlled milling. Unlike 3D printing, the milling process in subtractive and requires a tool. This process will a very high quality product, which is why it is commonly used in the industry. We have come across the milling process before, in order to manufacture circuits. In this case, we will built our own furniture, which require a bigger machine bed and a very stiff machine construction. Even though this technique is very powerful, it comes this some contraints. A design always has to respect the tools diameter and reachs, e. g. the tongue and groove design of press fits will mostly come in a "dogbone design" and the cutting depth is restrict in order to avoid collisions.

I will be designing my piece of furniture in Fusion. Our CNC router comes with a proprietary CAM software but of course, this process could be performed out of Fusion as well.

So, here are the tasks for Week 07:

Designing the bench

The idea was to design a bench, with has the silhouette of my initials (JK). The bench will consist of the two side part connected by threee reinforcing elements as well as 15 connectors to form the back and the seat

JK Bench design
image 01_Bench Step 1: Create a new component and start sketching (define parameters)
image 02_Bench Step 2: Extrude with the parameter 'Mat_Thickness', in this 18 mm
image 03_Bench Step 3: Sketch onto the extruded surface and create parametric slot
image 04_Bench Step 4: Extrude the slot (with the parametric thickness)
image 05_Bench_PathPattern Step 5: Extrude a pattern along the path depicted. Choose 15 instances, oriented in path direction
06_Bench_PathPattern_done 02_Bench Step 6: This results in slots that are orthogonal to path.
image 07_Bench_Connector Step 7: Now, design a simple connecting. Again respecting the existing parameters and an additional clearance (0.3 mm for smooth fit).
image 02_Bench Step 8: After extrusion, the result looks like this.
image 09_Bench_Reinforcer_done Step 9: The reinforcing element looks similar and connects the to sideframes.
image 10_Bench_Leg_position Step 10: Now, started assembling the components, copying the existing elements.
image 11_Copy_Leg_SetDistance Step 11: Set the correct (parametric) offset for the two sideframes.
image 12_AlignTool Step 12: Place the reinforcers using the align function.
image 13_CopyPasteConnectorAlign Step 13: Continue with the connectors and finish the assembly.
image 14_Project Step 14: Project the three parts on a new sketch.

There are different option to export the file.

image 15_ExportDXF Step 15: Preferred option - export the sketch as a *.dxf file
image 16_AlternativeCreateDrawingSaveAsPDF Alternative: create a drawing directly from the component.

CAM preparation

Some tweaking is still necessary in order to make the machining work. I used Rhino to remove double points and lines and completed the nesting operation. This cost me a lot of time to figure out as I did not worked with Rhino before and did not plant to. So, I tried all sorts of different tools from the internet. Initially, I laid a copy of each component flat in Fusion, using the align function. The nested parts were then projected onto a sketch and exported as a *.dxffile which the CNC router requires. I wanted to check the design in Inkscape but it could not visualize the splines of my model. So, I also tried create drafts from my parts using Fusion to export into Inkscape-compatible *.pdf files. Before I tried this, I also using a third party software called Kabeja to modify the broken *.dxf files for Inkscape.

To sum it up, I ended to export my three parts individually. My recommendation, the nesting can be done either in Rhino or in Fusion but some clean up should definitely be done after the export from Fusion. For this, my preferred option for this is Rhino. Join all curve elements, remove doubles and add internal and external elements to the respective layers.

image 17_CompleteNesting Step 17: Nesting operation
image 18_SetLayerColor Step 18: Add the internal and external cuts to different layers
image 19_Export_DXF Step 19: Export as a *.dxf

Bench production

The production ran smoothly, but the job took about 8 hours in the end. I choose a 18 mm multiplex sheet for the job and placed it on the bed. After turning on the vacuum, the sheet was hammered on the machine bed with a rubber mallet to have it sucked down by the underpressure. The cut to right depth, the tool length has to be set as well. For this purpose, a measurement tool with a button is placed underneath the drill bit. After x and y axis are homed, z is set to zero by lowering on the button.

image 1_RouterMaterial Place the material on the bed
image 2_TurnOnVacuum Turn on the vacuum
image 3_MeasureToolLength Measure the tool length

Now, the job can be launched. The 6 internal cuts are complemted in just a few minutes. The external cut, however, takes time. The tool cut a depth of 2.7 mm in each run, so that 7 runs are necessary to complete the cut. I used a FeedRate of 3000, a PlungeRate of 1000 and a SpindleSpeed 18000. The spindle direction is CW and tool diameter is 4 mm.

image External_Cut Settings internal cut
image External_Cut Settings external cut
image 4_InternalCut Perform the internal cut
image 5_ExternalCut Perform the external cut

The final result:

image BenchFinalResult Final result
image JoinTheFamily "Bigs" from Kamp Lintfort

I'm a hero!

image HeroShot_Week7 Hero shot

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